2D/3D image display

ABSTRACT

A display ( 8 ) comprises a display panel ( 9 ), a polariser ( 10 ), a polarisation rotator ( 13 ), and a scatterer ( 12 ) arranged to scatter light having a first polarisation as compared with light having a second polarisation. The display ( 8 ) can be switched between 2D and 3D modes by operating the polarisation rotator ( 13 ) accordingly. In 3D mode, the polarisation rotator ( 13 ) transmits light with relatively little or no change to its polarisation. Light transmitted by the scatterer ( 12 ) is then used to present a three-dimensional image ( 50 ). In 2D mode, the polarisation rotator ( 13 ) alters the polarisation of the light and light that is scattered by the scatterer ( 12 ) is used to present a two-dimensional image ( 51 ). The polarisation rotator ( 13 ) maybe arranged so that light incident on a first area thereof undergoes a different change in polarisation to light incident on a second area, in order to allow simultaneous presentation of 2D and 3D images ( 51, 50 ).

The present invention relates to display that is capable of presentingtwo-dimensional and three-dimensional images.

Light shutter display devices, such as liquid crystal displays (LCDs),in which a backlight is modulated on a pixel-by-pixel basis using aliquid crystal matrix, are well-known. Such devices generally produce atwo-dimensional (2D) image. However, rapid progress has been made in theresearch and development of three-dimensional (3D) displays. For reasonsof cost effectiveness and user convenience, display systems that do notrequire the user to wear special glasses in order to perceive a 3D imagehave been developed. These display systems are called autostereoscopicdisplays.

Autostereoscopic displays typically comprise a conventional displaypanel, such as a liquid crystal display (LCD), together with means forproviding a pair of images, in which one image is presented to aviewer's left eye and the other image is presented to the viewer's righteye. In some prior art displays, a 3D image is produced using alenticular screen placed in front of the display panel. In sucharrangements, the lenses focus light from different columns of pixels orsub-pixels into different regions of space, so that a viewer standing ata predetermined distance from the display panel will perceive a 3Dimage.

A less complex method for presenting 3D images uses a parallax barrier.Referring to FIG. 1, a conventional barrier-type autostereoscopicdisplay 1 comprises a display panel 2, a backlight 3 and a barrier 4.Typically, the barrier 4 is an opaque screen with a pattern of paralleltransparent lines or slits 5 a to 5 d and is placed either between thebacklight 3 and display panel 2 or in front of the display panel 2. Whenin use, light emitted by the backlight 3 is transmitted through theslits 5 a to 5 d of the barrier 4, so that the display panel 2 isilluminated by what is effectively a plurality of narrow elongate lightsources. Alternate columns of sub-pixels of the display panel 2 aredriven to display a left-eye image A and a right-eye image Brespectively. The sub-pixels have a pitch p_(d) and the display panel 2is positioned a distance c from the barrier 4, such that each “elongatelight source” illuminates one pair of sub-pixel columns. When thedisplay 1 is used by a viewer 6 at a distance d from the display panel2, the user's left and right eyes perceives the left-eye and right-eyeimages A, B respectively. However, as the barrier 4 blocks most of thelight generated by the backlight 3, this type of arrangement isinefficient.

Moreover, in both prior arrangements discussed above, the display panel2 is illuminated by vertical light lines. A small error in the pitch ofthe light lines with respect to the pitch p_(d) of the sub-pixels mayresult in visual artifacts in the displayed image, in the form of aMoiré pattern. One technique for avoiding such artifacts is to arrangethe backlight 3 so that the light lines are slanted relative to thecolumns of sub-pixels in the display panel 2, as described in respect ofa display comprising a lenticular screen in U.S. Pat. No. 6,064,424.This technique reduces the resolution of the display but the resolutionloss is distributed between the horizontal and vertical directions.

In the case of an autostereoscopic display having two views A, B, adisplayed 3D image can only be viewed from one perspective. For example,where the 3D image represents an object, the image displayed representsthe object when viewed from one angle. However, it is possible for adisplay to show the object from more than one perspective. In order toprovide a 3D image that is viewable from multiple perspectives and/or toallow the viewer greater freedom of movement, more views C, D etc. arerequired.

In a display where the light lines are not slanted with respect to thesub-pixel columns, the relationship between the pitch of the linesources p_(i) and the number of views m as follows,

$\begin{matrix}{P_{l} = {{\frac{a \cdot p_{d}}{a - p_{d}}m} \approx {p_{d} \cdot m}}} & \lbrack 1\rbrack\end{matrix}$

where p_(d) is the pitch of the sub-pixels and a is the requiredparallax between each view at the position of the user. The relationshipbetween the viewing distance d, the parallax a and the barrier-to-paneldistance c is given by equation 2,

$\begin{matrix}{a \approx {\frac{d}{c} \cdot p_{d}}} & \lbrack 2\rbrack\end{matrix}$

Regardless of whether an autostereoscopic display comprises a physicalbarrier or a lenticular screen, alternate pixels of the display panelare used to create different views A, B, C, D and so on. Therefore, a 3Dimage can only be displayed with a resolution that is relatively lowwhen compared with a 2D image displayed on the same apparatus. Whilethis may not be problematical when high resolution images are notrequired, this reduced resolution may not be acceptable for the displayof text or other 2D images. This problem has been overcome, to someextent, by providing displays that can be switched between 2D and 3Dimaging modes.

Where a switchable display includes a physical barrier, it may benecessary to include a switchable diffuser 7 between the barrier 4 anddisplay panel 2. When the display 1 is used in a 3D imaging mode, thediffuser 7 is switched into a transmissive state to allow lighttransmitted by the slits 5 a to 5 d to pass through. In a 2D imagingmode, the diffuser 7 is switched into a diffusing state, so that lightfrom the backlight 3 is scattered and the display panel 2 is uniformlyilluminated. However, as noted above, barrier arrangements areinefficient, as a significant proportion of the light generated by thebacklight 3 is lost. For instance, in 2D imaging modes, a significantproportion of the light may be scattered away from the display panel 2.In 3D mode, the light that does not enter the slits 5 a to 5 d iswasted.

In another prior switchable display, disclosed in WO 03/015424 A2, a LCDwithout an analysing polariser is provided. A lenticular screen,comprising an array of birefringent lenses, is positioned in front ofthe LCD, together with a liquid crystal (LC) cell, which acts as aswitchable half-wave plate, and an analysing polariser. The display isswitched between 2D and 3D imaging modes using the LC cell. When a 2Dimage is displayed, the LC cell alters the polarisation of light passingthrough it. When a 3D image is displayed, the display is operated sothat light passes through the LC cell without any change in itspolarisation. Light passing through the LC cell may then pass throughthe analysing polariser if it has the appropriate polarisation. However,this prior display works in different modes depending on whether 2D or3D images are displayed. When 2D images are displayed, the displayoperates in one of a “normally black” mode and a “normally white mode”and, when 3D images are displayed, the display operates in the other ofthe “normally black” mode and the “normally white” mode. In mostcircumstances, this prior display would be optimised for one of the“normally white” and “normally black” modes, so that operation in theother of the two modes results in relatively poor contrast and,therefore, reduced image quality. Furthermore, in this prior display,the lenticular screen must comprise an array of non-standard,polarisation-selective, microlenses. Such an array is expensive tomanufacture, due to the high cost of the required materials and thecomplexity of its fabrication.

The invention is intended to achieve one or more of the followingobjects: the provision of a display that is capable of displaying both2D and 3D images with a greater light efficiency than prior barriermethods, which may be less expensive and simpler to manufacture thanprior switchable displays, and the provision of a display that canpresent 2D and 3D images separately or simultaneously without decreasingthe resolution of the 2D image.

According to a first aspect of the invention, a display comprises adisplay panel, a polariser, a polarisation rotator that is selectivelyoperable to change the polarisation of light transmitted therethroughand a polarisation dependent scatterer configured to scatter lighthaving a first polarisation relative to light having a secondpolarisation, the polarisation rotator being operable so that, in afirst display mode, light scattered by the scatterer is used to presenta two-dimensional image and, in a second display mode, relativelyunscattered light is used to present a three-dimensional image.

When light is incident on the polarisation-dependent scatterer, lightwith a first polarisation is scattered, while light of a secondpolarisation passes through relatively unscattered. In some embodiments,where light of the first and second polarisations from a light line isincident on the scatterer, the scatterer scatters light with the firstpolarisation which may then provide uniform backlighting for thepresentation of a 2D image, while letting the light of the secondpolarisation pass through with little or no scattering, to providesuitable backlighting for presenting a 3D image, in the form of apattern of light lines.

The use of a polarisation-dependent scatterer instead of, say, abirefringent lenticular screen, confers a number of advantages over theprior art discussed above. For example, the scatterer may be formed ofless expensive materials and its manufacture considerably less complex.Furthermore, the scatterer does not need to be precisely aligned withthe light lines generated by the illumination system and/or sub-pixelsor pixels of the display panel, thereby simplifying the assembly of thedisplay.

Said light may be used to present a two-dimensional or three-dimensionalimage by providing illumination for the display panel or by conveyingimage information to one or more viewing zones.

The polarisation rotator may be configured so that, in the first displaymode, light entering the polarisation rotator, having a first inputpolarisation, has the second polarisation when leaving the polarisationrotator, while light entering the polarisation rotator, having a secondinput polarisation, has the first polarisation when leaving thepolarisation rotator, and, in the second display mode, light enteringthe polarisation rotator, having a first input polarisation, has thefirst polarisation when leaving the polarisation rotator, while lightentering the polarisation rotator, having a second input polarisation,has the second polarisation when leaving the polarisation rotator. Insome embodiments, the first and second input polarisations may be thesubstantially the same as the first and second polarisationsrespectively. Such a polarisation rotator may be operable so that lightentering a first area of the polarisation rotator having the first andsecond input polarisations, leave the polarisation rotator with thefirst and second polarisations respectively, while light entering asecond area of the polarisation rotator having the first and secondinput polarisations leave the polarisation rotator with the second andfirst polarisations respectively. This feature permits the display topresent 2D and 3D images simultaneously.

The display may comprise an illumination system arranged to generate aplurality of light lines comprising components having the firstpolarisation and components having the second polarisation. Optionally,a lenticular screen may also be provided and arranged to image the lightlines at a position between the lenticular screen and the display panel.In such an arrangement, the polariser may be positioned between saidillumination system and a lenticular screen, the lenticular screen beingarranged to create an image of the light lines by focussing thecomponents of having the first polarisation, at a position between thelenticular screen and the display panel. In both cases, the lenticularscreen may comprise an array of standard lenses configured to refractincident light regardless of its polarisation.

Alternatively, the display panel may be a light-emissive display device.

The display panel may be a liquid crystal device (LCD) in which a rearpolariser or a top polariser is not provided. Alternatively, the displaypanel may be a liquid crystal device and the polariser may be a rearpolariser of the liquid crystal device.

The scatterer may comprise a foil in which a plurality of elongateparticles are dispersed or a foil embossed with a grating pattern. Thefoil may be a stretched foil formed of PET or PEN.

The display may comprise a second scatterer, configured to scatter lighthaving the second polarisation relative to light having the firstpolarisation. When the display is operated in a 3D imaging mode, thesecond scatterer may scatter the light used to present the 3D image,thereby increasing the sizes of the viewing zones.

The invention also provides a device comprising such a display, forexample a communication device, such as a mobile telephone, a computingdevice or a display device for or in audio/visual equipment, and use ofsuch a display or device.

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a known autostereoscopic displayarrangement for producing multiple views of an image;

FIG. 2 is a schematic diagram of a display according to a firstembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIGS. 3 a and 3 b depict a scattering element suitable for use in thedisplay of FIG. 2;

FIG. 4 depicts another scattering element suitable for use in thedisplay of FIG. 2;

FIG. 5 depicts the light emerging from a polarisation rotator of thedisplay of FIG. 2 when 2D and 3D images are displayed simultaneously;

FIG. 6 is a schematic diagram of an illumination system suitable for usein the display of FIG. 2;

FIG. 7 is a schematic diagram a display according to a second embodimentof the invention showing light paths through the display when operatingin 3D and 2D imaging modes;

FIG. 8 is a schematic diagram of a display according to a thirdembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 9 is a schematic diagram of a display according to a fourthembodiment of the showing light paths through the display when operatingin 3D and 2D imaging modes;

FIG. 10 is a schematic diagram of a display according to a fifthembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 11 is a schematic diagram of a display according to a sixthembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 12 is a schematic diagram of a display according to a seventhembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 13 is a schematic diagram of a display according to an eighthembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 14 is a schematic diagram of a display according to a ninthembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 15 is a schematic diagram of a display according to a tenthembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 16 is a schematic diagram of a display according to an eleventhembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 17 is a schematic diagram of a display according to a twelfthembodiment of the invention showing light paths through the display whenoperating in 3D and 2D imaging modes;

FIG. 18 is a schematic diagram of a mobile telephone comprising thedisplay of FIG. 2;

FIG. 19 is a schematic diagram of a personal digital assistantcomprising the display of FIG. 2; and

FIG. 20 depicts a desktop monitor comprising the display of FIG. 2.

FIG. 2 depicts a display 8, comprising a display panel 9, in which atwo-dimensional array of sub-pixels is defined, a polariser 10, alenticular screen 11, a polarisation-dependent scatterer 12 and aswitchable polarisation rotator 13. The display 8 also comprises anillumination system 14, arranged to generate backlighting for thedisplay panel 9, as will be described in detail later. In thisparticular example, each light line causes a column of four sub-pixelsin the display panel 9 to be illuminated. Each of the sub-pixels withinthe column may present a different view, for example, views A, B, C andD, so that a viewer positioned at a suitable location may perceive a 3Dimage by registering an appropriate pair of views.

In this particular embodiment, the display panel 9 and the polarisationrotator 13 each comprise a layer of electro-optically active material,such as a liquid crystal material, sandwiched between twolight-transmissive substrates (not shown). In the case of a liquidcrystal layer, the operation of the layer may be based on, for example,a twisted nematic (TN), super-twisted nematic (STN), vertically alignednematic (VAN), optically compensated birefringence (OCB), in-planeswitching nematics (IPS) or ferro-electric effect for modulating apolarisation direction of incident light. The layer of electro-opticallyactive material is sandwiched between two substrates (not shown), madefrom a transparent material such as, for example, glass, silicon dioxide(SiO₂), quartz or a suitable plastic material.

The display panel 9 is subdivided into an array of sub-pixels and isprovided with an active matrix or a passive matrix arrangement (notshown) for driving the pixels to display an image, in a manner wellknown per se. The display panel 9 also comprises a front polariser, oranalyser, (not shown), which transmits light exiting the liquid crystallayer with an appropriate polarisation, and retarders (not shown) but,unlike conventional display panels, no rear polariser is provided.

The polarisation rotator 13 is arranged so that it can operate in afirst mode, in which the pixels of the polarisation rotator 13 maychange the polarisation of light passing through them from a first inputpolarisation to a first output polarisation, referred to hereafter asS-polarisation, and from a second input polarisation to a second outputpolarisation, referred to hereafter as P-polarisation. The polarisationrotator 13 can also operate in a second mode, in which incident lighthaving the first input polarisation leaves the polarisation rotator 13with the second output polarisation, that is, P-polarisation, whileincident light having the second input polarisation leaves thepolarisation rotator 13 with the first output polarisation,S-polarisation. In this particular example, when operating in the secondmode, the polarisation rotator 13 changes to polarisation of lightpassing through it from P- to S-polarisation and vice versa, while, inthe first mode, the polarisation of light passing through thepolarisation rotator 13 is unchanged.

If required, the polarisation rotator 13 may be subdivided into an arrayof pixels, as in this particular embodiment. The polarisation rotator 13is thus provided with an active matrix or a passive matrix arrangement(not shown) for driving the pixels. By driving the pixels accordingly,the polarisation rotator 13 may be switched between first and secondmodes. Such an arrangement also permits different pixels of thepolarisation rotator 13 to be operated in different modessimultaneously, so that light passing through one region of thepolarisation rotator 13 is subjected to a change in polarisation whilelight passing through another region is unaffected.

In this example, the display panel 9 and polarisation rotator 13. Thecontroller 15 is arranged to receive image signals i and to drive thesub-pixels of the display panel 9 and polarisation rotator 13accordingly, by supplying appropriate signals to their respective activematrix or passive matrix arrangements. If required, the controller 15may also control the illumination system 14.

The polarisation-dependent scatterer 12 comprises a foil that scattersincident light that is linearly polarised in a first direction to a muchgreater degree than light that is linearly polarised in a seconddirection. In this example, the scatterer 12 scatters S-polarised light,while P-polarised light undergoes relatively little, or no, scattering.

Suitable scattering foils are disclosed in WO97/32223 A1, whichdescribes a film comprising a substantially non-birefringent phase ofpolymeric particles, dispersed within a continuous birefringentpolymeric matrix. The refractive indices of the dispersed phase andpolymeric matrix are similar along two orthogonal directions but differsignificantly from one another along a third orthogonal direction.Incident light that is polarised parallel to the third orthogonaldirection is scattered to a much greater degree than incident light thatis polarised parallel to the other orthogonal directions.

An example of a suitable scattering element for the scatterer 12 isshown in FIGS. 3 a and 3 b, in the form of a foil 16 comprisingcore-shell particles 16 a dispersed in a poly ethylene terephtalate(PET) matrix, in a ratio of 1:9 by weight. In this example, thecore-shell particles 16 a have an initial diameter of approximately 200nm, but are extruded and stretched along a given direction S by a factorof 4. FIG. 3 a is a cross-sectional view of the foil 16 perpendicular tothe stretching direction S, while FIG. 3 b shows a cross-section of thefoil parallel to the stretching direction S.

Light is incident on the scatterer 12 along a direction that isperpendicular to the stretch direction S. In FIG. 3 b, the incidentlight is directed into the page. Light polarised in a direction parallelto the stretching direction S which, in this embodiment, is S-polarisedlight, is scattered. However, light polarised along an orthogonaldirection P, here, P-polarised light, passes through the foil 16 withrelatively little, or no, scattering when compared with the S-polarisedlight.

FIG. 4 depicts another example of a suitable scattering element. A foil17, of PET, poly ethylene naphtalate (PEN) or a similar polymer isextruded and stretched by a factor of 4 to 5, so that its refractiveindex n1 along the stretch direction S is higher than its refractiveindex n2 perpendicular to the stretch direction S. For example, for aPET foil, the refractive indices n1 and n2 may be 1.7 and 1.53respectively. For a PEN foil, the refractive indices n1 and n2 may be1.85 and 1.56 respectively. The foil 17 is then embossed with amicrograting pattern and provided with a coating 18 with a refractiveindex that is substantially matched to the refractive index n2 of thefoil 17, perpendicular to the stretching direction S.

While FIG. 4 shows a foil 17 embossed with a regular pattern, it is notnecessary for the micrograting pattern to have a constant period. Infact, in an alternative scatterer, an embossed surface may be configuredwith a variety of sloped facets in order to provide refracting anddiffusing effects.

The scatterer 12 is preferably configured so that light is scatteredpredominantly in a narrow range of angles in the forward direction,towards the display panel 9. In this manner, backscattering, which wouldresult in diffuse background illumination and degrade the contrast ofthe light lines when the display is in 3D mode, may be reduced.

The lenticular screen 11 comprises an array of standard lenses thatrefract incident light regardless of its polarisation. However, if theincident light is polarised in a direction that is neither parallel nororthogonal to the lens surface, the refraction may alter itspolarisation. If this is the case, it may be necessary to arrange thepolariser 10 and/or the scatterer 12, so that they are appropriatelyorientated. However, the alignment of the lenticular screen 11 with thepolariser 10 and scatterer 12 need not be exact, as a minor misalignmentwill not prevent the functioning of the display. In embodiments wherethe lenticular screen 11 is placed at a slant to the sub-pixel columns,for example, to avoid the generation of Moiré effects and other visualartifacts, the polariser 10 and scatterer 12 must be orientatedaccordingly. In both cases, the illumination system 14 must be arrangedto generate light lines that are aligned with the lenticular screen 11.

For the purposes of the following discussion, P-polarisation refers tolinear polarisation along a direction parallel to the plane of thefigures, while polarisation orthogonal to the plane of the figures willbe referred to as S polarisation. However, it should be noted that thetwo polarisation directions need not be those described and also thatarrangements are possible in which the action of the scatterer 12 on Pand S polarised light is interchanged, if necessary, with correspondingchanges to the polariser 10, without affecting the performance of theinvention.

FIG. 2 depicts the light paths followed by light lines emitted by theillumination system 14 at positions 14 a, 14 b when the display 8 is ina 3D imaging mode. The light lines generated by the illumination system14 includes both P- and S-polarised light. However, the S-polarisedcomponents of the light are largely blocked by the polariser 10, and sothe light that passes through the polariser 10 for imaging by thelenticular screen 11 is generally P-polarised.

The lenticular screen 11 focuses the light so as to produce an image ofthe light lines at a position between the lenticular screen 11 and thedisplay panel 9. This imaging reduces the effective distance between theillumination system 14 and display panel 9. In other words, the effectof this arrangement is equivalent to generating the light lines at areduced distance c′ from the display panel 9, as compared with theactual distance c between the illumination system 14 and the displaypanel 9.

The P-polarised light enters the polarisation rotator 13, which, in thisexample, is operated in its second mode, and so allows P-polarised lightto be transmitted without any change to its polarisation. Here, thescatterer 12 is largely translucent for P-polarised light. The displaypanel 9 is thus illuminated by P-polarised light lines, permitting thepresentation of a 3D image in a “normally white” mode.

FIG. 2 also shows the light path followed by a light line emitted by theillumination system 14 at position 14 e when the display 8 is in a 2Dimaging mode. In this figure, P-polarised light is shown using solidlines, while S-polarised light is represented by dashed lines.

Here, P-polarised components of the light in the light lines passthrough the polariser 10 and is imaged by the lenticular screen 11.However, the polarisation rotator 13 is switched into its first mode, sothat the P-polarised light emerges from the polarisation rotator 13 asS-polarised light. The S-polarised light is scattered by the scatterer12 in random directions, thereby providing uniform illumination for thedisplay panel 9 for presentation of a 2D image. In this case, thedisplay panel 9 is driven in a “normally black” mode. However, thedisplayed image can be electronically inverted, by inverting imagingsignals controlling the sub-pixels of the display panel 9, in a mannerwell known per se, so that a viewer will perceive the image as if itwere displayed in a “normally white” mode.

Where the polarisation rotator 13 is divided into an array of pixels, asdiscussed above, it may be operated in both the first and second modesimultaneously, so that, for example, light passing through a firstregion of the polarisation rotator 13 may be subjected to a change inpolarisation, while light passing through a second region is unaffected.As a result, suitable illumination is provided to allow the display 8 topresent a 2D image and a 3D image simultaneously. For example, a 2Dimage, such as text, can be displayed at the same time as a 3D image,without a decrease in its resolution. An example of the illuminationrequired for the simultaneous display of 2D and 3D images is shown inFIG. 5, in which light passing through the first region provides uniformillumination within a corresponding first area 19 a of the display panel9, while light passing through the second region forms a pattern oflight lines for illuminating a corresponding second area 19 b of thedisplay panel 9. In this manner, the display 8 can present a 3D image“window” within a 2D image or vice versa.

A suitable illumination system 14 for the display 8 is depicted indetail in FIG. 6. The illumination system 14 comprises a light source20, such as a fluorescent rod lamp and, optionally, a reflector 21. Thedisplay panel 9 is also shown in this figure, although interveningcomponents of the display 8, such as the polariser 10, lenticular screen11, scatterer 12 and polarisation rotator 13, are omitted.

Light emitted by the light source 18 enters a waveguide 22, whichcomprises a diffusing layer 23 comprising an array of diffusing portions24 a to 24 f. Examples of suitable diffusive materials include a polymerdispersed liquid crystal (PDLC), which is diffusive in the absence of anelectric field and plastics material containing particles of anothermaterial for scattering incident light, such as Polymethyl methacrylate(PMMA) containing embedded titanium dioxide particles.

The diffusing portions 24 a to 24 f are separated by non-diffusingportions, 25 a to 25 g, which comprise a transparent material that isfree from scattering particles. The diffusing layer 23 is sandwichedbetween substrates 26, 27. The substrates 26, 27 are made from atransparent material such as glass, silicon dioxide (SiO₂), quartz or asuitable plastic material. Preferably, the refractive indices of thenon-diffusing regions and substrates 26, 27 are substantially equal.

An end face 28 of the waveguide 22 is arranged to receive light emittedby the light source 20 directly and also reflected light from the lightsource 20, if a reflector 21 is provided. The light propagates throughthe waveguide 22 and undergoes total internal reflection at the outerfaces of the substrates 26, 27. However, light incident on a diffusingportion 24 a to 24 f is scattered in a random direction and may leavethe waveguide 20 through an exit face 29 that is arranged to face thedisplay panel 9. The light that leaves the waveguide 22 through the exitface 29 forms a pattern of light lines. Examples of paths followedwithin the waveguide 22 are shown using dashed lines.

The dimensions of the portions 24 a to 24 f, 25 a to 25 g are selectedso that cross-talk between views A, B, C, D is limited to an acceptablelevel. In this particular example, the portions 25 a to 25 g have awidth of approximately 405 μm, portions 24 a to 24 f have a width ofapproximately 50 μm. However, the dimensions used in other embodimentsof the invention will depend on the type of display 8 and its sub-pixelsize. As a general guide, the portions 24 a to 24 f, 25 a to 25 g areconfigured so that light lines are produced with a width selected from arange of 10 to 800 μm, with a pitch of between 100 μm to 10 mm. Thewidth of the light line will be less than, or equal to, half the pitchin order to limit cross-talk.

Light may continue to propagate through the waveguide 22 until it isscattered by a diffusing portion 24 a to 24 f and exits the waveguide 22through one of the exit face 29, a face 30 of the substrate 26 remotefrom the display panel 9 or an end face, for example, end face 28, ofthe waveguide 20. In spite of the light loss through the faces of thewaveguide 20 other than the exit face 29, the light efficiency of thewaveguide 22 compares favourably with prior art barrier arrangements,such as that shown in FIG. 1, in which light lines are formed byblocking and discarding unwanted light. This light cannot be recoveredwithout degrading the contrast of the light lines. However, in analternative arrangement, such losses are reduced by providing alight-reflective surface (not shown) on, or instead of, substrate 27. Asthe diffusing layer 21 is situated close to the light-reflectivesurface, this arrangement increases light efficiency while generating apattern of light lines with a reasonable contrast.

Further embodiments of the present invention will now be described. Asthe displays comprise many, or all of, the components of the display ofFIG. 2, the same reference numerals will be used to indicate likecomponents.

FIG. 7 depicts a display 31 according to a second embodiment of theinvention. Like the display 8 of FIG. 2, the display 31 comprises adisplay panel 9, a polariser 10, a lenticular screen 11, apolarisation-dependent scatterer 12, a polarisation rotator 13 and anillumination system 14. The display 31 differs from the display 8 of thefirst embodiment in that the polariser 10 is located between thelenticular screen 11 and polarisation rotator 13.

The illumination system 14 emits light lines including both P- andS-polarised components. The light lines are imaged by the lenticularscreen 11. The P-polarised components of the light within the lightlines is then transmitted by the polariser 10, while the S-polarisedcomponents are blocked.

When the display 31 is used to present a 3D image, as shown in FIG. 8 inrespect of the light lines emitted at positions 14 a and 14 b of theillumination system 14, the polarisation rotator 13 in its second mode.Thus, light lines of P-polarised light emerge from the polarisationrotator 13 and pass through the scatterer 12, undergoing little or noscattering to illuminate the display panel 9.

FIG. 7 also depicts the light path of a light line emitted at position14 e of the illumination system 14, when the display 31 is used topresent a 2D image. In this case, the polarisation rotator 13 isoperated in its first mode. Therefore, the light lines emerging from thepolarisation rotator 13 are S-polarised and are scattered by thescatterer 12, providing uniform illumination for the display panel 9.

FIG. 8 depicts a display 32 according to a third embodiment of theinvention. The display 32 differs from the display 8 of FIG. 2 in thatthe display panel 9 is a LCD which is equipped with a rear polariser 33.The rear polariser 33 is used in place of the polariser 10 of the firstembodiment. In addition, the scatterer 12 is located between thelenticular screen 11 and polarisation rotator 13.

The illumination system 14 emits light lines of both P- andS-polarisation, which are imaged by the lenticular screen 11. TheS-polarised components of the light lines are then scattered by thescatterer 12, while the P-polarised light passes through relativelyunscattered.

When the display 32 is used to present a 3D image, as shown in FIG. 8 inrespect of the light lines emitted at positions 14 a and 14 b of theillumination system 14, the polarisation rotator 13 is operated in itssecond mode. Thus, light lines of P-polarised light pass through therear polariser 33 to illuminate the display panel 9, while the scatteredS-polarised light is blocked by the rear polariser 33.

FIG. 8 also depicts the light path of a light line emitted at position14 e of the illumination system 14 when the display 32 is used topresent a 2D image. Here, the polarisation rotator 13 is operated in itsfirst mode. Therefore, the light lines emerging from the polarisationrotator 13 are S-polarised and are blocked by the rear polariser 33,while the scattered light leaving the polarisation rotator 13 isP-polarised. The P-polarised scattered light passes through the rearpolariser 33, providing uniform illumination for the display panel 9.

A display 34 according to a fourth embodiment of the invention is shownin FIG. 9. As in the previous embodiments, the illumination system 14emits light lines comprising both P- and S-polarised components.S-polarised light is blocked by the polariser 10, while P-polarisedlight passes through and enters the polarisation rotator 13.

When the display 33 is presenting a 3D image, the polarisation rotator13 is operated in its second mode, so that the light lines leaving thepolarisation rotator 13 are P-polarised. The P-polarised light lines areimaged by the lenticular screen 11 and pass through the scatterer 12with little or no scattering, to illuminate the display panel 9. Theoperation of the display 33 in a 3D imaging mode is shown in FIG. 9 inrespect of the light lines emitted at positions 14 a and 14 b of theillumination system 14.

When the display 33 is presenting a 2D image, the polarisation rotator13 it is operated in its first mode, so that the light lines emergingfrom the polarisation rotator 13 are S-polarised. The light lines arethus scattered by the scatterer 12, to provide uniform illumination forthe display panel 9. The operation of the display 33 when in a 2Dimaging mode is depicted in FIG. 9 for a light line emitted at position14 e of the illumination system 14.

FIG. 10 depicts a display 35 according to a fifth embodiment of theinvention. The display 35 differs from that shown in FIG. 8 in thepositioning of the polarisation-dependent scatterer 12. In thisembodiment, the scatterer 12 is located between the polarisation rotator13 and lenticular screen 11.

As described above, in relation to the previous embodiments, theillumination system 14 emits light lines comprising both P- andS-polarised components. The S-polarised components are blocked by thepolariser 10, while the P-polarised components are transmitted.

When the display 35 is presenting a 3D image, the polarisation rotator13 is operated in its second mode. Thus, the P-polarised light linespass through the scatterer 12 with little or no scattering and areimaged by the lenticular screen 11 to illuminate the display panel 9, asshown in respect of the light line emitted at position 14 b of theillumination system 14.

When the display 35 is presenting a 2D image, the light lines emergingfrom the polarisation rotator 13 are S-polarised and so are scattered bythe scatterer 12, before being focussed by the lenticular screen 11.This is depicted in FIG. 10 for a light line emitted from position 14 eof the illumination system 14. The scattered light provides uniformillumination for the display panel 9.

FIG. 11 depicts a display 36 according to a sixth embodiment of theinvention. As in the third embodiment described above, the display 36comprises a display panel 9 in the form of a LCD with a rear polariser33, which is used in place of a separate polariser. In addition, thescatterer 12 is positioned between the illumination system 14 andpolarisation rotator 13.

The operation of the display 36 in a 3D imaging mode will now bedescribed with reference to an example light line that is emitted atposition 14 b of the illumination system 14. P-polarised components ofthe light line pass through the scatterer 12 with little or noscattering and enter the polarisation rotator 13. Here, the polarisationrotator 13 is operated in its second mode and so does not alter thepolarisation of light passing therethrough. The P-polarised light lineis then imaged by the lenticular screen 11, passes through the rearpolariser 33 and illuminates the display panel 9.

Meanwhile, S-polarised components of the light line are scattered by thescatterer 12. The S-polarised scattered light passes through thepolarisation rotator 13 and is imaged by the lenticular screen 11 beforebeing blocked by the rear polariser 33.

When the display 36 is presenting a 2D image, the scatterer 12 transmitsthe P-polarised light with little or no scattering in the light linesand scatters the S-polarised light, as is shown in FIG. 11 for a lightline emitted at position 14 e of the illumination system 14. Thepolarisation rotator 13 is operated in its first mode. Thus, incidentP-polarised light lines emerge from the polarisation rotator asS-polarised light lines, which are imaged by the lenticular screen 11and then blocked by the rear polariser 33. The scattered S-polarisedlight entering the polarisation rotator 13 emerges with P-polarisationand is imaged by the lenticular screen 11 before passing through therear polariser 33 to illuminate the display panel 9.

FIG. 12 depicts a display 37 according to a seventh embodiment of theinvention. The display 37 is similar to the display 36 of FIG. 11.However, in this arrangement, the display panel 9 can be illuminatedwith light lines having a relatively large opening angle compared withthe previously described embodiments. This is achieved by providing asecond polarisation-dependent scatterer 38. As in the previousembodiments, the scatterer 12 is configured to scatter S-polarisedlight. However, the second scatterer 38 is arranged to scatterP-polarised light while allowing S-polarised light to pass throughrelatively unscattered.

The operation of this arrangement as described above in relation to thedisplay 36 of FIG. 11 for light lines emitted by the illumination system14 at positions 14 b and 14 e, with respect to their passage through thescatterer 12, polarisation rotator 13 and lenticular screen 11.

When the display 37 is operating in a 3D imaging mode, P-polarised lightlines imaged by the lenticular screen 11 are scattered by the secondscatterer 38 but then pass through the rear polariser 33 to illuminatethe display panel 9. Due to the effect of the second scatterer 38, theopening angle of the light lines illuminating the display panel 9 isincreased. Meanwhile, S-polarised light passes through the secondscatterer 38 and is blocked by the rear polariser 33. The paths followedthe P- and S-polarised components of a light line emitted at position 14b of the illumination system 14 are shown in FIG. 12.

When the display 37 is operating in a 2D imaging mode, the light linesemerging from the polarisation rotator 13 have S-polarisation. This isshown in FIG. 12 for a light line emitted from position 14 e of theillumination system 14. The light lines are imaged by the lenticularscreen 11 and pass through the second scatterer 38 with little or noscattering. However, being S-polarised, the light lines are blocked bythe rear polariser 33. The scattered light emerging from thepolarisation rotator 13 is P-polarised and is imaged by the lenticularscreen 11 before being scattered by the second scatterer 38. Thescattered light then passes through the rear polariser 33 to provideuniform illumination for the display panel 9.

FIG. 13 shows a display 39 according to a eighth embodiment of theinvention. The display 39 differs from the display 36 of FIG. 11 in thatthe positions of the lenticular screen 11 and polarisation rotator 13are interchanged.

As in the previous embodiments, light lines comprising P- andS-polarised components are generated by the illumination system 14. Thescatterer 12 transmits P-polarised light with little or no scatteringbut scatters S-polarised light. The resulting P-polarised light linesand S-polarised scattered light are focussed by the lenticular screen 11before entering the polarisation rotator 13.

When the display 39 is presenting a 3D image, the polarisation rotator13 is operated in its second mode, and so the P-polarised light linesemerge from the polarisation rotator 13 and pass through rear polariser33 to illuminate the display panel 9. However, the S-polarised scatteredlight is blocked by the rear polariser 33. FIG. 13 shows the light pathsfollowed by the P- and S-polarised components of a light line emitted atposition 14 b by the illumination system 14.

With reference to the light line emitted at position 14 e by theillumination system 14, when the display 39 is presenting a 2D image,the P-polarised light lines become S-polarised when passing through thepolarisation rotator 13 and so are blocked by the rear polariser 33. Thepolarisation rotator 13 changes the polarisation of the scatteredS-polarised light to P-polarisation. The scattered light then passesthrough the rear polariser 33 to illuminate the display panel 9.

FIG. 14 depicts a display 40 according to a ninth embodiment of theinvention. The display 40 is similar to the display 34 of FIG. 9 butdiffers in that the lenticular screen 11 of the fourth embodiment is notprovided.

While the omission of the lenticular screen provides a cost advantageover prior arrangements, the light lines generated by the illuminationsystem 14 are not focussed within the display 40. As a result, the lightlines appear to be generated at a position further away from the displaypanel 9, when compared with the displays of the previous embodiments, sothat relatively smaller viewing zones are created by the display 40. Inorder to counteract this effect, it may be necessary for the LCD of thedisplay panel 9 to comprise relatively thin substrates. For example, ifthe display 40 forms part of a mobile telephone (not shown), the typicaldistance d between a viewer and the display 40 is 400 mm. In order tocorrespond with the left and right eyes of potential viewers, theviewing zones for multiple views A, B have a parallax a of approximately65 mm apart at the viewing distance d. If the pixel pitch p_(d) is 45μm, the distance c of the illumination system 14 from the display panel9 can, be determined using Equation [2] above to be approximately 270μm. This is significantly lower than the typical thickness of thesubstrate of a LCD in a mobile telephone, which is at least 400 μm.

When the display 40 is presenting a 3D image, the P-polarised componentsof the light lines, for example, the light lines emitted at positions 14a and 14 b of the illumination system 14, pass through the polariser 10and through polarisation rotator 13 without any change to theirpolarisation. The P-polarised light lines then pass through thescatterer 12 to illuminate the display panel 9. The S-polarisedcomponents of the light lines are blocked by the polariser 10.

When the display 40 is presenting a 2D image, P-polarised components ofthe light lines, such as the light line emitted at position 14 e of theillumination system 14, pass through the polariser 10, while S-polarisedcomponents is blocked. The resulting P-polarised light lines then passthrough polarisation rotator 13 and emerge as S-polarised light lineswhich are scattered by the scatterer 12. The S-polarised scattered lightthus provides uniform illumination for the display panel 9.

In addition to the cost advantage noted above, the omission of alenticular screen may provide greater flexibility in the display ofimages. If the illumination system 14 is operable to allow changes inthe positions 14 a, 14 b, 14 e at which light lines are generated, forexample, under the control of the controller 15, the absence of alenticular screen may allow the positions of the viewing zones formultiple views A, B to be varied to allow for movement by a viewer.

FIG. 15 depicts a display 41 according to a tenth embodiment of theinvention. The display 41 is similar to the display 40 of FIG. 14 butdiffers in that the positions of the scatterer 12 and polariser 10 areinterchanged.

When the display 41 is presenting a 3D image, the polarisation rotator13 is operated in its second mode. Hence, P-polarised components of thelight lines, pass through the scatterer 12 and the polarisation rotator13 without little or no scattering and, in this example, without asignificant change in their polarisation. The P-polarised light linesthen pass through the polariser 10 to illuminate the display panel 9, asshown in FIG. 15 in respect of light lines emitted at positions 14 a and14 b of the illumination system 14. The S-polarised components arescattered by the scatterer 12 and pass through the polarisation rotator13 with its polarisation unchanged before being blocked by the polariser10.

When the display 41 is presenting a 2D image, the P-polarised componentsof the light lines pass through the scatterer 12 and polarisationrotator 13, emerging from the polarisation rotator 13 as S-polarisedlight which is blocked by the polariser 10. Meanwhile, the S-polarisedcomponents of the light lines are scattered by the scatterer 12 andemerge from the polarisation rotator 13 as P-polarised light. Thescattered P-polarised light passes through the polariser 10 andilluminates the display panel 9. This is depicted in FIG. 15 in respectof a light line emitted at position 14 e of the illumination system 14.

It should be noted that, in this particular embodiment, the scatterer 12must be positioned at a sufficient distance from the illumination system14 to allow the light scattered by the scatterer 12 to be substantiallyuniform across the display panel 9 when the display 41 is operated in a2D imaging mode.

FIG. 16 depicts a display 42 according to an eleventh embodiment of theinvention. The display 42 comprises a display panel 9 in the form of aLCD with a rear polariser 33. However, a top polariser, or an analysingpolariser, for selectively transmitting light emerging from thesub-pixels 42 of the LCD is not provided. The display 42 also comprisesa lenticular screen 11, a polarisation-dependent scatterer 12, apolarisation rotator 13 and polariser 10, arranged in front of thedisplay panel 9, so that they act on light emerging from the sub-pixels43. This arrangement differs from the embodiments described above, inwhich the equivalent components were positioned to the rear of thedisplay panel 9.

The display panel 9 is illuminated with a conventional backlight 43,that generates substantially uniform illumination. Depending on theconfiguration of the rear polariser 33, light with either P-polarisationor S-polarisation enter the display panel 9 and illuminate thesub-pixels 44.

When the display 42 is presenting a 3D image, the sub-pixels 44 arearranged so that P-polarised light emerges from the display panel 9, asshown for sub-pixels 44 a and 44 b in FIG. 16. The P-polarised light isimaged into viewing zones by the lenticular screen 11 and passes throughthe scatterer 12 with little or no scattering. The P-polarised lightthen passes through the polarisation rotator 13, which is operated totransmit light without altering its polarisation, and the polariser 10,and then leaves the display 42, to present multiple views A, B inrespective viewing zones.

The presentation of a 2D image by the display 42 will now be described,with reference to the light paths for light from sub-pixels 44 c and 44d as shown in FIG. 16. S-polarised light emerges from the sub-pixels 44,which is focussed by the lenticular screen 11 and then scattered by thescatterer 12, before entering the polarisation rotator 13. TheS-polarised light emerges from the polarisation rotator 13 withP-polarisation and so passes through the polariser 10 and leaves thedisplay panel 9.

A display 45 according to a twelfth embodiment of the invention is shownin FIG. 17. The display 45 is similar to the display 42 of FIG. 16, butdiffers in that the positions of the lenticular screen 11 and scatterer12 are interchanged.

When the display 45 is presenting a 3D image, the sub-pixels 44 arearranged so that P-polarised light emerges from the display panel 9, asshown for sub-pixels 44 a and 44 b in FIG. 16. The P-polarised lightpasses through the scatterer 12 with little or no scattering and is thenis focussed by the lenticular screen 11 so as to generate images ofviews A, B in their respective viewing zones. The P-polarised light thenpasses through the polarisation rotator 13, without changing itspolarisation. The P-polarised light then passes through the polariser 10and leaves the display 45, to present the multiple views A, B.

When the display 45 is presenting a 2D image, S-polarised light emergesfrom the sub-pixels 44, as shown for sub-pixels 44 c and 44 d in FIG.16. The S-polarised light is scattered by the scatterer 12 before beingfocussed by the lenticular screen 11. The polarisation rotator 13 causesthe light to become P-polarised. The P-polarised light can thus passthrough the polariser 10 and leave the display panel 9.

In this particular embodiment, the scattering profile of the scatterer12 is limited in order to avoid a reduction in resolution when a 2Dimage is displayed, due to blurring of the images from adjacentsub-pixel columns 44 c, 44 d. Depending on the configuration of thedisplay 42, a suitable scattering angle may be in the range of 5° to20°.

The displays 8, 14, 32, 34, 35, 36, 37, 39, 40, 41, 42, 45 describedabove may be used in any device arranged to display images. FIGS. 18, 19and 20 depict example devices comprising the display 8 shown in FIG. 2.

FIG. 18 depicts a mobile telephone handset 46, comprising a userinterface, in the form of display 8 and keypad 47, a microphone 48 andspeaker 49. The display 8 is configured with a resolution adequate forthe display of images and video and may, if required, be capable ofdisplaying colour images. In FIG. 18, the display 8 is arranged topresent a 3D picture 50, comprising two views A and B. In an area aroundthe 3D picture 50, a 2D image, such as text 51 or wallpaper, isdisplayed.

FIG. 19 depicts a personal digital assistant (PDA) 52 comprising thedisplay 8 in a user interface that further comprises keys 47. FIG. 19shows examples of displayed images in the form of a 3D image 50 and 2Dtext 51.

FIG. 20 depicts a desktop monitor 53 comprising the display 8, fordisplaying images based on image data output by a personal computer (PC)54. The display 8, keyboard 55 and, if required, a mouse device (notshown) provide a user interface for the PC 54. In this figure, thedesktop monitor 52 is shown when displaying a 3D image 50 and 2D text 51simultaneously.

While FIGS. 18, 19 and 20 depicted a mobile telephone handset 46, PDA 52and desktop monitor 53 comprising a display 8 according to theinvention, the display of the present invention is not limited to use inthese particular devices. The display 8 may be incorporated in, forexample, other communication devices, games consoles and devices,televisions, automotive displays and displays for or in audio/visualequipment, whether fixed or portable.

Furthermore, a display according to any one of the second to twelfthembodiments could be provided while the devices shown in FIG. 18, 19 or20, in place of the display 8 of FIG. 2. However, as described in detailabove, if the display lacks a lenticular screen 11, as in the eighth andninth embodiments, it may be necessary to use relatively thin substratesin the display panel 9.

From reading the present disclosure, other variations and modificationswill be apparent to persons skilled in the art. Such variations andmodifications may involve equivalent and other features which arealready known in the design, manufacture and use of electronic devicescomprising liquid crystal displays, alternative display devices ortransflectors and component parts thereof and which may be used insteadof or in addition to features already described herein.

In the above described embodiments, P-polarised light is used in 3Dimaging and S-polarised light in 2D imaging. However, the displays maybe arranged so that S-polarised light is used for 3D imaging andP-polarised light for 2D imaging, by providing an appropriate polariser10 and using a scatterer 12 that scatters P-polarised light buttransmits S-polarised light without scattering and, where the displaypanel 9 is a LCD, by changing the orientation of the retarders andpolarisers 33 of the display panel 9.

In each of the above described embodiments, the polarisation rotator 13is configured so that light passes through it without any change inpolarisation when the display is in a 3D imaging mode. However, this isnot necessarily the case. The polarisation rotator 13 may be arranged toapply a fixed minimum rotation, so that, in 3D mode, the minimumrotation is applied while, in 2D mode, the polarisation is rotated by adifferent amount, for example, by the minimum rotation plus 90 degrees.Any polarisers 10, 33 arranged to receive light that has passed throughsuch a polarisation rotator 13 must be configured to admit and blocklight with such rotated polarisations.

While the polarisation rotator 13 in the above embodiments is a LC cell,other types of switchable polarisation rotator may be used, includingmechanical polarisation rotators.

In the above described embodiments, 3D images are presented in a“normally white” mode, while 2D images are presented in a “normallyblack” mode. These modes can be interchanged. In any case, the effectsof the inverted contrast on the displayed image can be counteracted byelectronically inverting the image for display in one of the “normallywhite” and “normally black” modes, in a manner well known per se.

The features of the above embodiments have been described in relation tosub-pixels 44 of the display panel 9 and their pitch p_(d). However, ifrequired, the above described displays could be configured to display 3Dimages using alternate columns of pixels, rather than columns ofsub-pixels 44. This may be particularly appropriate where the displaypanel 14 is a monochrome display.

Although the simultaneous display of 2D and 3D images is described inrespect of the display 8 of FIG. 2, this effect can be achieved usingany of the other described displays, where the polarisation rotator 13can be operated to change the polarisation of light passing through itin one or more selected areas only.

The placement of the lenticular screen 11, where provided, so that it isslanted with respect to the sub-pixel columns, is discussed above onlyin relation to the display 8 of FIG. 2. However, such placement may beused in any of the embodiments comprising such a lenticular screen 11.Similarly, if a slanted positioning is not required, the lenticularscreen 11 of any of the first to eighth, eleventh and twelfthembodiments may be aligned with the sub-pixel columns. Whichever is thecase, the alignment of any polarisers 10, 33 and the scatterer 12 withthe lenticular screen 11 must be ensured.

In displays 40, 41 without lenticular screens, the illumination system14 may be arranged so that the light lines it produces are slanted withrespect to the columns of sub-pixels, in order to avoid the generationof visual artifacts, such as Moiré patterns.

The displays 32, 36, 37, 39 of FIGS. 8, 11, 12 and 13 each comprise adisplay panel 9 with a rear polariser 33. However, if required, thesecomponents may be replaced with a display panel 9 without a rearpolariser 32 and a separate polariser 10 provided.

Furthermore, although the examples described relate to displayscomprising a LCD display panel 9, other embodiments of the invention mayutilise other types of light shutter display panels 9, includingelectrophoretic displays, electrochromic displays, electro-wettingdisplays and micromechanical displays, such as micro-electro-mechanicalsystems (MEMS). In the displays 42, 45 of the eleventh and twelfthembodiments, the display panel 9 may be a light emissive display device,such as a cathode ray tube (CRT), an array of light emitting diodes, anorganic light emitting diode (OLED) display, a field emissive display(FED) and so on, in which case, the illumination system 14 may beomitted.

Although Claims have been formulated in this Application to particularcombinations of features, it should be understood that the scope of thedisclosure of the present invention also includes any novel features orany novel combination of features disclosed herein either explicitly orimplicitly or any generalisation thereof, whether or not it relates tothe same invention as presently claimed in any Claim and whether or notit mitigates any or all of the same technical problems as does thepresent invention. The Applicants hereby give notice that new Claims maybe formulated to such features and/or combinations of such featuresduring the prosecution of the present Application or of any furtherApplication derived therefrom.

1. A display (8), comprising: a display panel (9); a polariser (10); apolarisation rotator (13) that is selectively operable to change thepolarisation of light transmitted therethrough; and a polarisationdependent scatterer (12) configured to scatter light having a firstpolarisation relative to light having a second polarisation; thepolarisation rotator (13) being operable so that: in a first displaymode, light scattered by the scatterer (12) is used to present atwo-dimensional image (51); and in a second display mode, relativelyunscattered light is used to present a three-dimensional image (50). 2.A display according to claim 1, wherein said light used to present atwo-dimensional or three-dimensional image (51, 50) providesillumination for the display panel (9).
 3. A display according to claim1, wherein said light used to present a two-dimensional orthree-dimensional image (51, 50) conveys image information to one ormore viewing zones.
 4. A display (8) according to claim 1, wherein: inthe first display mode, light entering the polarisation rotator (13),having a first input polarisation, has the second polarisation whenleaving the polarisation rotator (13), while light entering thepolarisation rotator (13), having a second input polarisation, has thefirst polarisation when leaving the polarisation rotator (13); and inthe second display mode, light entering the polarisation rotator (13),having a first input polarisation, has the first polarisation whenleaving the polarisation rotator (13), while light entering thepolarisation rotator (13), having a second input polarisation, has thesecond polarisation when leaving the polarisation rotator (13).
 5. Adisplay (8) according to claim 4, wherein: the polarisation rotator (13)is configured so that the first input polarisation is substantially thesame as the first polarisation and the second input polarisation issubstantially the same as the second polarisation.
 6. A display (8)according to claim 4, wherein: said polarisation rotator (13) isoperable so that light entering a first area of the polarisation rotator(13) and having the first and second input polarisations, leave thepolarisation rotator (13) with the first and second polarisationsrespectively, while light entering a second area of the polarisationrotator (13) and having the first and second input polarisations leavethe polarisation rotator (13) with the second and first polarisationsrespectively.
 7. A display (8) according to claim 1, comprising: anillumination system (14) arranged to generate a plurality of light linescomprising components having the first polarisation and componentshaving the second polarisation.
 8. A display (8) according to claim 7,comprising: a lenticular screen (11) for imaging the light lines,arranged so that images of the light lines are created at a positionbetween the lenticular screen (11) and the display panel (9).
 9. Adisplay (8) according to claim 7, wherein: said polariser (10) islocated between said illumination system (14) and a lenticular screen(11), the lenticular screen (11) being arranged to create an image ofthe light lines by focussing the components having the firstpolarisation, at a position between the lenticular screen (11) and thedisplay panel (9).
 10. A display according to claim 1, wherein: saiddisplay panel (9) is a light-emissive display.
 11. A display accordingto claim 1, wherein the display panel (9) is a liquid crystal device inwhich a rear polariser is not provided.
 12. A display according to claim1, wherein the display panel (9) is a liquid crystal device in which atop polariser is not provided.
 13. A display according to claim 1,wherein the display panel (9) is a liquid crystal device and saidpolariser is a rear polariser (33) of the liquid crystal device.
 14. Adisplay (8) according to claim 1, wherein said scatterer (12) comprisesa foil (16) in which a plurality of elongate particles (16 a) issuspended.
 15. A display (8) according to claim 1, wherein saidscatterer (12) comprises a foil (17) embossed with a grating pattern.16. A display (8) according to claim 14, wherein said foil (16, 17) is astretched foil of poly ethylene terephtalate or poly ethylenenaphtalate.
 17. A display according to claim 1, comprising: a secondscatterer (38), configured to scatter light having the secondpolarisation relative to light having the first polarisation.
 18. Use ofa display according to claim 1 for displaying a two-dimensional image(51) and a three-dimensional image (50).
 19. Use of a display accordingto claim 6, wherein said two-dimensional image (51) and saidthree-dimensional image (50) are displayed simultaneously.
 20. Acommunication device (46) comprising a display (8) according to claim 1.21. A communication device (46) according to claim 20, in the form of amobile telephone.
 22. A computing device (52) comprising a display (8)according to claim
 1. 23. A computing device according to claim 22, inthe form of a laptop computer.
 24. A computing device (52) according toclaim 22, in the form of a personal digital assistant.
 25. Audio/visualequipment (53) comprising a display (8) according to claim
 1. 26.Audio/visual equipment (53) according to claim 25, in the form of amonitor arranged to present images generated by a computer (54).